Thanks a lot Lyedge.
After I read your reply, I went out to apply braking in reverse. I felt the braking is a little bit better now but the braking is still noticeably different than before - ie. pedal distance is longer. I noticed you said '...try driving the car backwards and apply the brakes a few times'. and reply from biglow also said '...倒幾次車就行了。倒車時會自動調整.'. For me, I probably had applied the reserve braking at least 100 times or maybe more in my drive way (in low speed). So I wonder if it literally only take a few reserve braking as you said, like 3 or 5 times, or it takes a lot more reserve braking. Maybe I did something wrong?